Systems and methods for constant voltage control and constant current control

ABSTRACT

System and method for regulating a power conversion system. A system controller for regulating a power conversion system includes a first controller terminal, a second controller terminal and a third controller terminal. The system controller is configured to receive an input signal at the first controller terminal and turn on or off a switch based on at least information associated with the input signal to adjust a primary current flowing through a primary winding of the power conversion system, receive a first signal at the second controller terminal from the switch, and charge a capacitor through the third controller terminal in response to the first signal.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201210099930.8, filed Mar. 31, 2012, incorporated by reference hereinfor all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for voltageregulation and current regulation. Merely by way of example, theinvention has been applied to a power conversion system. But it would berecognized that the invention has a much broader range of applicability.

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system. The power conversion system 100 includes a primarywinding 110, a secondary winding 112, a power switch 120, a currentsensing resistor 130, a rectifying diode 160, a capacitor 162, anisolated feedback component 114, and a controller 170. The controller170 includes an under-voltage-lockout component 172, apulse-width-modulation generator 174, a gate driver 176, aleading-edge-blanking (LEB) component 178, and anover-current-protection (OCP) component 180. For example, the powerswitch 120 is a bipolar transistor. In another example, the power switch120 is a field effect transistor.

As shown in FIG. 1, the power conversion system 100 uses a transformerincluding the primary winding 110 and the secondary winding 112 toisolate an AC input voltage 102 on the primary side and an outputvoltage 104 on the secondary side. Information related to the outputvoltage 104 is processed by the isolated feedback component 114 whichgenerates a feedback signal 154. The controller 170 receives thefeedback signal 154, and generates a gate-drive signal 156 to turn onand off the switch 120 in order to regulate the output voltage 104.

To achieve good output current control, the power conversion system 100often needs additional circuitry in the secondary side, which usuallyresults in high cost. Moreover, the required output current sensingresistor in the secondary side usually reduces the efficiency of thepower conversion system 100.

FIG. 2 is a simplified diagram showing another conventional flybackpower conversion system. The power conversion system 200 includes aprimary winding 210, a secondary winding 212, an auxiliary winding 214,a power switch 220, a current sensing resistor 230, two rectifyingdiodes 260 and 268, two capacitors 262 and 270, and two resistors 264and 266. For example, the power switch 220 is a bipolar transistor. Inanother example, the power switch 220 is a MOS transistor.

Information related to the output voltage 250 can be extracted throughthe auxiliary winding 214 in order to regulate the output voltage 250.When the power switch 220 is closed (e.g., on), the energy is stored inthe secondary winding 212. Then, when the power switch 220 is open(e.g., off), the stored energy is released to the output terminal, andthe voltage of the auxiliary winding 214 maps the output voltage on thesecondary side as shown below.

$\begin{matrix}{V_{FB} = {\frac{R_{2}}{R_{1} + R_{2}} \times V_{aux}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where V_(FB) represents a feedback voltage 274, and V_(aux) represents avoltage 254 of the auxiliary winding 214. R₁ and R₂ represent theresistance values of the resistors 264 and 266 respectively.

A switching period of the switch 220 includes an on-time period duringwhich the switch 220 is closed (e.g., on) and an off-time period duringwhich the switch 220 is open (e.g., off). For example, in a continuousconduction mode (CCM), a next switching cycle starts before thecompletion of a demagnetization process associated with the transformerincluding the primary winding 210 and the secondary winding 212. Thus,the actual length of the demagnetization process before the nextswitching cycle starts is limited to the off-time period of the switch.In another example, in a discontinuous conduction mode (DCM), a nextswitching cycle does not start until a period of time after thedemagnetization process has completed. In yet another example, in aquasi-resonant (QR) mode or a critical conduction mode (CRM), a nextswitching cycle starts shortly after the completion of thedemagnetization process.

FIG. 3(A) is a simplified conventional timing diagram for the flybackpower conversion system 200 that operates in the continuous conductionmode (CCM). The waveform 302 represents the voltage 254 of the auxiliarywinding 214 as a function of time, the waveform 304 represents asecondary current 278 that flows through the secondary winding 212 as afunction of time, and the waveform 306 represents a primary current 276that flows through the primary winding 210 as a function of time.

For example, a switching period, T_(s), starts at time t₀ and ends attime t₂, an on-time period, T_(on), starts at the time t₀ and ends attime t₁, and an off-time period, T_(off), starts at the time t₁ and endsat the time t₂. In another example, t₀≦t₁≦t₂.

During the on-time period T_(on), the power switch 220 is closed (e.g.,on), and the primary current 276 flows through the primary winding 210and increases from a magnitude 308 (e.g., I_(pri) _(—) ₀ at t₀) to amagnitude 310 (e.g., I_(pri) _(—) _(p) at t₁) as shown by the waveform306. The energy is stored in the secondary winding 212, and thesecondary current 278 is at a low magnitude 312 (e.g., approximatelyzero) as shown by the waveform 304. The voltage 254 of the auxiliarywinding 214 keeps at a magnitude 314 (e.g., as shown by the waveform302).

At the beginning of the off-time period T_(off) (e.g., at t₁), theswitch 220 is open (e.g., off), the primary current 276 is reduced fromthe magnitude 310 (e.g., I_(pri) _(—) _(p)) to a magnitude 316 (e.g.,approximately zero) as shown by the waveform 306. The energy stored inthe secondary winding 212 is released to the output load. The secondarycurrent 278 increases from the magnitude 312 (e.g., approximately zero)to a magnitude 318 (e.g., I_(sec) _(—) _(p)) as shown by the waveform304. The voltage 254 of the auxiliary winding 214 increases from themagnitude 314 to a magnitude 320 (e.g., as shown by the waveform 302).

During the off-time period T_(off), the switch 220 remains open, theprimary current 276 keeps at the magnitude 316 (e.g., approximatelyzero) as shown by the waveform 306. The secondary current 278 decreasesfrom the magnitude 318 (e.g., I_(sec) _(—) _(p)) to a magnitude 322(e.g., I_(sec) _(—) ₂ at t₂) as shown by the waveform 304. The voltage254 of the auxiliary winding 214 decreases from the magnitude 320 to amagnitude 324 (e.g., as shown by the waveform 302).

At the end of the off-time period T_(off) (e.g., t₂), a next switchingcycle starts before the demagnetization process is completed. Theresidual energy reflects back to the primary winding 210 and appears asan initial primary current, I_(pri) _(—0) , at the beginning of the nextswitching cycle.

For example, the primary current 276 and the secondary current 278satisfy the following equations:

I _(sec) _(—) _(p) =N×I _(pri) _(—) _(p)  (Equation 2)

I _(sec) _(—) ₂ =N×I _(pri) _(—) ₀  (Equation 3)

where I_(sec) _(—) _(p) represents the secondary current 278 when theoff-time period T_(off) starts, and I_(sec) _(—) ₂ represents thesecondary current 278 when the off-time period T_(off) ends.Additionally, I_(pri) _(—) _(p) represents the primary current 276 whenthe on-time period T_(on) ends, I_(pri) _(—) ₀ represents the primarycurrent 276 when the on-time period T_(on) starts, and N represents aturns ratio between the primary winding 210 and the secondary winding212.

The output current 252 can be determined based on the followingequation:

$\begin{matrix}{I_{out} = {\frac{1}{2} \times \frac{1}{T} \times {\int_{0}^{T}{\left( {I_{sec\_ p} + I_{{sec\_}2}} \right) \times \frac{T_{demag}}{T_{s}}\ {t}}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

where I_(out) represents the output current 252, T represents anintegration period, T_(s) represents a switching period, and T_(demag)represents the duration of the demagnetization process within theswitching period. For example, T_(demag) is equal to the off-time periodT_(off) in the CCM mode.

Combining the equations 2, 3 and 4, one can obtain the followingequation.

$\begin{matrix}{I_{out} = {\frac{N}{2} \times \frac{1}{T} \times {\int_{0}^{T}{\left( {I_{{pri}{\_ p}} + I_{{pri\_}0}} \right) \times \frac{T_{demag}}{T_{s}}\ {t}}}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

Referring to FIG. 2, the resistor 230, in combination with othercomponents, generates a current-sensing voltage signal 272 (e.g.,V_(cs)) which is related to the primary current 276. For example, theoutput current 252 can be determined according to the followingequation:

$\begin{matrix}{I_{out} = {\frac{N}{2} \times \frac{1}{R_{s} \times T} \times {\int_{0}^{T}{\left( {V_{{cs}\; 1} + V_{{cs}\; 0}} \right) \times \frac{T_{demag}}{T_{s}}\ {t}}}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where V_(cs0) represents the current-sensing voltage signal 272 when anon-time period starts during a switching cycle, V_(cs1) represents thecurrent-sensing voltage signal 272 when the on-time period ends duringthe switching cycle, and R_(s) represents the resistance of the resistor230.

In another example, the output current 252 can be determined based onthe following equation:

$\begin{matrix}{I_{out} = {\frac{N}{2} \times \frac{1}{R_{s} \times K} \times {\sum\limits_{1}^{K}\; {\left( {{V_{{cs}\; 1}(n)} + {V_{{cs}\; 0}(n)}} \right) \times \frac{T_{demag}(n)}{T_{s}(n)}}}}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

where n corresponds to the n^(th) switching cycle, V_(cs0)(n) representsa magnitude of the current-sensing voltage signal 272 when an on-timeperiod T_(on) starts in the n^(th) switching cycle, and V_(cs1)(n)represents a magnitude of the current-sensing voltage signal 272 whenthe on-time period ends in the n^(th) switching cycle. Additionally, Krepresents the number of switching cycles that are included in thecalculation. For example, K can be infinite; that is, the calculation ofEquation 7 can include as many switching cycles as needed. As shown inEquations 6 and 7, the output current 252 may be regulated (e.g., bekept constant) based on information associated with the current-sensingvoltage signal 272.

FIG. 3(B) is a simplified conventional timing diagram for the flybackpower conversion system 200 that operates in the discontinuousconduction mode (DCM). The waveform 332 represents the voltage 254 ofthe auxiliary winding 214 as a function of time, the waveform 334represents a secondary current 278 that flows through the secondarywinding 212 as a function of time, and the waveform 336 represents aprimary current 276 that flows through the primary winding 210 as afunction of time.

For example, as shown in FIG. 3(B), a switching period, T_(s), starts attime t₃ and ends at time t₆, an on-time period, T_(on), starts at thetime t₃ and ends at time t₄, a demagnetization period, T_(demag) startsat the time t₄ and ends at time t₅, and an off-time period, T_(off),starts at the time t₄ and ends at the time t₆. In another example,t₃≦t₄≦t₅≦t₆. In DCM, the off-time period, T_(off), is much longer thanthe demagnetization period, T_(demag).

During the demagnetization period T_(demag), the switch 220 remainsopen, the primary current 276 keeps at a magnitude 338 (e.g.,approximately zero) as shown by the waveform 336. The secondary current278 decreases from a magnitude 340 (e.g., I_(sec) _(—) _(p) at t₄) asshown by the waveform 334. The demagnetization process ends at the timet₅ when the secondary current 278 has a low magnitude 342 (e.g., zero).The secondary current 278 keeps at the magnitude 342 for the rest of theswitching cycle.

A next switching cycle starts after the completion of thedemagnetization process (e.g., at the time t₆). For example, littleresidual energy reflects back to the primary winding 210 and the primarycurrent 276 (e.g., I_(pri) _(—) ₀ at t₆) at the beginning of the nextswitching cycle has a low magnitude 344 (e.g., zero).

FIG. 3(C) is a simplified conventional timing diagram for the flybackpower conversion system 200 that operates in the quasi-resonant (QR)mode or the critical conduction mode (CRM). The waveform 352 representsthe voltage 254 of the auxiliary winding 214 as a function of time, thewaveform 354 represents a secondary current 278 that flows through thesecondary winding 212 as a function of time, and the waveform 356represents a primary current 276 that flows through the primary winding210 as a function of time.

For example, as shown in FIG. 3(C), a switching period, T_(s), starts attime t₇ and ends at time t₁₀, an on-time period, T_(on) starts at thetime t₇ and ends at time t₈, a demagnetization period, T_(demag) startsat the time t₈ and ends at time t₉, and an off-time period, T_(off),starts at the time t₈ and ends at the time t₁₀. In another example,t₇≦t₈≦t₉≦t₁₀. In the CRM mode, the demagnetization period, T_(demag), isslightly shorter than the off-time of the switch, T_(off).

The demagnetization process ends at the time t₉ when the secondarycurrent 278 has a low magnitude 358 (e.g., zero). The secondary current278 keeps at the magnitude 358 for the rest of the switching cycle. Anext switching cycle starts (e.g., at t₁₀) shortly after the completionof the demagnetization process. The primary current 276 has a lowmagnitude 360 (e.g., zero) at the beginning of the next switching cycle.

The power conversion system 200 often cannot achieve satisfactorydynamic responses with low standby power when the output load changesfrom no load to full load. Hence, it is highly desirable to improvetechniques for voltage regulation and current regulation of a powerconversion system.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for voltageregulation and current regulation. Merely by way of example, theinvention has been applied to a power conversion system. But it would berecognized that the invention has a much broader range of applicability.

According to one embodiment, a system controller for regulating a powerconversion system includes a first controller terminal, a secondcontroller terminal and a third controller terminal. The systemcontroller is configured to receive an input signal at the firstcontroller terminal and turn on or off a switch based on at leastinformation associated with the input signal to adjust a primary currentflowing through a primary winding of the power conversion system,receive a first signal at the second controller terminal from theswitch, and charge a capacitor through the third controller terminal inresponse to the first signal.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. The system controller is configured togenerate a drive signal at the first controller terminal to turn on oroff a switch to adjust a primary current flowing through a primarywinding of the power conversion system, receive a first signal at thesecond controller terminal from the switch, and generate a detectionsignal associated with a demagnetization process of the primary windingof the power conversion system based on at least information associatedwith the first signal.

According to yet another embodiment, a system for regulating a powerconversion system includes a system controller, a feedback component anda capacitor. The system controller includes a current regulationcomponent and a drive component, the system controller further includinga first controller terminal connected to the current regulationcomponent and a second controller terminal connected to the drivecomponent. The feedback component is connected to the first controllerterminal and configured to receive an output signal associated with asecondary winding of a power conversion system. The capacitor includes afirst capacitor terminal and a second capacitor terminal, the firstcapacitor terminal being connected to the first controller terminal. Thecurrent regulation component is configured to receive at least a currentsensing signal and affect a feedback signal at the first controllerterminal based on at least information associated with the currentsensing signal, the current sensing signal being associated with aprimary current flowing through a primary winding of the powerconversion system. The drive component is configured to processinformation associated with the current sensing signal and the feedbacksignal, generate a drive signal based on at least information associatedwith the current sensing signal and the feedback signal, and send thedrive signal to a switch through the second controller terminal in orderto adjust the primary current.

In another embodiment, a method for regulating a power conversion systemby at least a system controller including a first controller terminal, asecond controller terminal and a third controller terminal includes:receiving an input signal at the first controller terminal, turning onor off a switch based on at least information associated with the inputsignal to adjust a primary current flowing through a primary winding ofthe power conversion system, receiving a first signal at the secondcontroller terminal from the switch, and charging a capacitor throughthe third controller terminal in response to the first signal.

In yet another embodiment, a method for regulating a power conversionsystem by at least a system controller including a first controllerterminal and a second controller terminal include: generating a drivesignal at the first controller terminal to turn on or off a switch toadjust a primary current flowing through a primary winding of the powerconversion system, receiving a first signal at the second controllerterminal from the switch, and generating a detection signal associatedwith a demagnetization process of the primary winding of the powerconversion system based on at least information associated with thefirst signal.

Many benefits are achieved by way of the present invention overconventional techniques. Certain embodiments of the present inventionprovide a system and method for charging a supply capacitor through apower switch during a start-up process using a large resistor to reducepower dissipation. Some embodiments of the present invention provide asystem and method for demagnetization detection using a voltage at aswitching node. Certain embodiments of the present invention provide asystem and method for sampling a current sensing voltage in the middleof an on-time period to avoid sampling two separate voltage signals inorder to reduce sampling errors. Some embodiments of the presentinvention provide a system and method for sampling a current sensingvoltage in the middle of an on-time period (e.g., ½ T_(on)) to avoid aninitial spike voltage problem when sampling the current sensing voltageat the beginning of the on-time period.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system.

FIG. 2 is a simplified diagram showing another conventional flybackpower conversion system.

FIG. 3(A) is a simplified conventional timing diagram for the flybackpower conversion system in FIG. 2 that operates in the continuousconduction mode (CCM).

FIG. 3(B) is a simplified conventional timing diagram for the flybackpower conversion system in FIG. 2 that operates in the discontinuousconduction mode (DCM).

FIG. 3(C) is a simplified conventional timing diagram for the flybackpower conversion system in FIG. 2 that operates in the quasi-resonant(QR) mode or the critical conduction mode (CRM).

FIG. 4( a) is a simplified diagram showing a power conversion systemwith a controller according to an embodiment of the present invention.

FIG. 4( b) is a simplified diagram showing a power conversion systemwith a controller according to another embodiment of the presentinvention.

FIG. 5 is a simplified timing diagram for demagnetization detection ofthe power conversion system 400 shown in FIG. 4( a) or the powerconversion system shown in FIG. 4( b) operating in the discontinuousconduction mode (DCM) according to an embodiment of the presentinvention.

FIG. 6 is a simplified diagram showing a power conversion system with acontroller according to yet another embodiment of the present invention.

FIG. 7 is a simplified diagram showing certain components of thedemagnetization component as part of the power conversion system shownin FIG. 6 according to an embodiment of the present invention.

FIG. 8( a) is a simplified timing diagram for the demagnetizationdetection component as part of the power conversion system shown in FIG.6 operating in the discontinuous conduction mode (DCM) according to anembodiment of the present invention.

FIG. 8( b) is a simplified timing diagram for the demagnetizationdetection component as part of the power conversion system operating inthe continuous conduction mode (CCM) according to another embodiment ofthe present invention.

FIG. 9 is a simplified diagram showing certain components of the signalprocessing component as part of the power conversion system shown inFIG. 6 according to an embodiment of the present invention.

FIG. 10 is a simplified diagram showing certain components of the lowpass filter as part of the power conversion system shown in FIG. 6according to an embodiment of the present invention.

FIG. 11 is a simplified diagram showing certain components of the lowpass filter as part of the power conversion system shown in FIG. 6according to another embodiment of the present invention.

FIG. 12 is a simplified diagram showing certain components of acontroller according to an embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for voltageregulation and current regulation. Merely by way of example, theinvention has been applied to a power conversion system. But it would berecognized that the invention has a much broader range of applicability.

FIG. 4( a) is a simplified diagram showing a power conversion systemwith a controller according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications.

The power conversion system 400 includes a controller 402, a primarywinding 404, a secondary winding 406, a current sensing resistor 408, anisolated feedback component 419, two capacitors 410 and 414, a resistor412, and a power switch 416. The controller 402 includes a switch 418, acurrent-control component 420, a leading-edge-blanking (LEB) component422, an over-current-protection (OCP) component 424, apulse-width-modulation (PWM) component 426, a gate driver 428, anunder-voltage-lockout (UVLO) component 430, a reference signal generator432, an oscillator 434, a resistor 484, and a diode 486. Further, thecontroller 402 includes six terminals 488, 490, 492, 494, 496 and 498.For example, the power switch 416 is a bipolar transistor. In anotherexample, the power switch 416 is a field effect transistor (e.g., aMOSFET), and sustains a high drain-source voltage (e.g., larger than 600volts). In yet another example, the switch 418 is a bipolar transistor.In yet another example, the switch 418 is a field effect transistor, andsustains a relatively low drain-source voltage (e.g., less than 40volts). In yet another example, the controller 402 is on a chip, and theterminals 488, 490, 492, 494, 496 and 498 are pins on the chip. In yetanother example, the capacitor 410 is off the chip, and coupled betweenthe terminal 490 (e.g., terminal VDD) and a chip-ground voltage 489.

According to one embodiment, information related to the output voltage436 is processed by the isolated feedback component 419 which generatesa feedback signal 438. For example, the controller 402 receives thefeedback signal 438 at the terminal 498 (e.g., terminal FB), andgenerates a gate-drive signal 440 at the terminal 492 (e.g., terminalGate) to drive the switch 416 in order to regulate the output voltage436.

According to another embodiment, when the power conversion system 400starts up, the resistor 412 receives an input voltage 444, and a voltage446 at the terminal 492 (e.g., terminal Gate) increases in magnitude.For example, the switch 416 is closed (e.g., on), and the switch 418 isopen (e.g., off). In another example, a current 448 flows through theswitch 416, the resistor 484 and the diode 486 to charge the capacitor410, and as a result, a voltage 450 at the terminal 490 (e.g., terminalVDD) increases in magnitude. In yet another example, if the start-upprocess of the power conversions system 400 completes and the voltage450 is higher than the voltage 446, there is no longer a current flowingthrough the resistor 484 and the diode 486 to charge the capacitor 410.In yet another example, the resistance of the resistor 412 can beincreased to reduce power dissipation. In yet another example, after thestart-up process of the power conversion system 400 completes, the powerswitches 416 and 418 are controlled to be turned on and off at the sametime in normal operations. In yet another example, after the start-upprocess of the power conversion system 400 completes, the switch 418 isalways kept on in normal operations.

As discussed above and further emphasized here, FIG. 4( a) is merelyexamples, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the switch 416 is included in acontroller 401 as part of a power conversion system, as shown in FIG. 4(b).

FIG. 4( b) is a simplified diagram showing a power conversion systemwith a controller according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,the power conversion system shown in FIG. 4( b) operates similarly asthe power conversion system 400.

Referring back to FIG. 2, the demagnetization process can be detectedbased on the voltage 254 of the auxiliary winding 214, for which anadditional terminal is often needed on the controller chip. In contrast,a demagnetization process can be detected using voltages at terminal 452and/or terminal 454 of the switch 416 in the power conversion system 400shown in FIG. 4( a) or the power conversion system shown in FIG. 4( b),according to certain embodiments.

FIG. 5 is a simplified timing diagram for demagnetization detection ofthe power conversion system 400 shown in FIG. 4( a) or the powerconversion system shown in FIG. 4( b) operating in the discontinuousconduction mode (DCM) according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications.

The waveform 502 represents a voltage of the terminal 452 of the switch416 as a function of time, the waveform 504 represents a voltage of theterminal 454 of the switch 416 as a function of time, and the waveform506 represents a slope of the voltage of the terminal 454 of the switch416 as a function of time. For example, an on-time period, T_(on),starts at time t₁₁ and ends at time t₁₂, and a demagnetization period,T_(demag), starts at the time t₁₂ and ends at time t₁₃. In anotherexample, t₁₁≦t₁₂≦t₁₃.

According to one embodiment, during the on-time period (e.g., T_(on)),both the switch 416 and the switch 418 are closed (e.g., on). Forexample, a primary current 456 that flows through the primary winding404 increases in magnitude. In another example, the voltage of theterminal 452 (e.g., V_(D)) and the voltage of the terminal 454 (e.g.,V_(SD)) have low magnitudes (e.g., as shown by the waveform 502 and thewaveform 504 respectively).

According to another embodiment, if both the switch 416 and the switch418 are open (e.g., off), the primary current 456 reduces to a lowmagnitude (e.g., zero), and the demagnetization process starts. Forexample, during the demagnetization period T_(demag), the voltage of theterminal 452 (e.g., V_(D)) is approximately at a magnitude 508 (e.g., asshown by the waveform 502), and the voltage of the terminal 454 (e.g.,V_(SD)) is approximately at a magnitude 510 (e.g., as shown by thewaveform 504).

According to yet another embodiment, the demagnetization process ends atthe time t₁₃. For example, the voltage of the terminal 454 (e.g.,V_(SD)) decreases rapidly in magnitude (e.g., as shown by the waveform504). In another example, the voltage drop at the terminal 454 is due toparasitic capacitance and the inductance of the transformer thatincludes the primary winding 404 and the secondary winding 406. Thus,the demagnetization can detected based on information associated withthe voltage of the terminal 454 (e.g., V_(SD)). Though the abovediscussion is based on the timing diagram of the power conversion system400 operating in the DCM mode, the scheme for demagnetization detectionapplies to the power conversion system 400 operating in the CCM mode orin the CRM mode according to certain embodiments.

FIG. 6 is a simplified diagram showing a power conversion system with acontroller according to yet another embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications.

The power conversion system 600 includes a controller 602, a primarywinding 604, a secondary winding 606, a current sensing resistor 608, anisolated feedback component 610, and a power switch 616. The controller602 includes a switch 618, a signal processing component 620, a signalgenerator 621, a leading-edge-blanking (LEB) component 622, antransconductance amplifier 624, a capacitor 626, a low pass filter 612,a comparator 614, a slope compensation component 615, a demagnetizationdetection component 660, a gate drive component 628, a logic controlcomponent 662, a voltage regulation component 664, and an oscillator634. Further, the controller 602 includes four terminals, 692, 694, 696and 698. For example, the power switch 616 is a bipolar transistor. Inanother example, the power switch 616 is a field effect transistor. Inyet another example, the switch 618 is a field effect transistor. In yetanother example, the primary winding 604, the secondary winding 606, thecurrent sensing resistor 608, the isolated feedback component 610, thepower switch 616, the switch 618, and the LEB component 622 are the sameas the primary winding 404, the secondary winding 406, the currentsensing resistor 408, the isolated feedback component 419, the powerswitch 416, the switch 418, and the LEB component 422. In yet anotherexample, a current regulation loop includes the signal processingcomponent 620, the transconductance amplifier 624, the capacitor 626,the demagnetization detection component 660, and the low pass filter612.

According to one embodiment, information related to the output voltage636 is processed by the isolated feedback component 610 which generatesa feedback signal 638. For example, the controller 602 receives thefeedback signal 638 at the terminal 698 (e.g., terminal FB), andgenerates a gate-drive signal 640 at the terminal 692 (e.g., terminalGate) to drive the switch 616 in order to regulate the output voltage636. In another example, the demagnetization component 660 receives thegate-drive signals 640 and 641 and a voltage signal 630 through theterminal 694 (e.g., terminal SD), and generates ademagnetization-detection signal 666. In yet another example, thedemagnetization-detection signal 666 has a pulse width of T_(demag) foreach switching cycle, where T_(demag) represents the duration of ademagnetization process in a switching cycle. In yet another example,the switches 616 and 618 are controlled to be turned on and off at thesame time in normal operations. In yet another example, the switch 618is always kept on in normal operations.

According to yet another embodiment, a primary current 656 that flowsthrough the primary winding 604 is sensed using the resistor 608. Forexample, the resistor 608 generates, through the terminal 696 and withthe leading-edge blanking component 622, a current sensing signal 632.In another example, for each switching cycle, the signal processingcomponent 620 receives the current sensing signal 632 and thedemagnetization-detection signal 666, and outputs a signal 668 that isequal to (I_(pri) _(—) _(p)+I_(pri) _(—) ₀)×T_(demag) where I_(pri) _(—)₀ represents the primary current 656 when an on-time period starts in aswitching cycle and I_(pri) _(—) _(p) represents the primary current 656when the on-time period ends in the switching cycle. In yet anotherexample, for each switching cycle, the signal generator 621 receives areference signal 670 and a clock signal 672 and outputs a signal 674that is equal to I_(ref)×T_(s), where I_(ref) represents a predeterminedreference current and T_(s) represents a switching period.

According to another embodiment, an integrator that includes thetransconductance amplifier 624 and the capacitor 626 receives both thesignal 668 and the signal 674, and outputs a signal 676 to the low passfilter 612. For example, the magnitude difference of the signals 668 and674 (e.g., I_(ref)×T_(s)−(I_(pri) _(—) _(p)+I_(pri) _(—) ₀)×T_(demag))is amplified and integrated by the transconductance amplifier 624 andthe capacitor 626. In yet another example, the low pass filter 612outputs a signal 678 to the comparator 614. In yet another example, thecomparator 614 also receives a signal 680 from the slope compensationcomponent 615 and outputs a signal 682 to the logic control component662. In yet another example, the voltage regulation component 664receives the feedback signal 638 and the current sensing signal 632 andoutputs signals 686 and 688 to the logic control component 662. In yetanother example, the logic control component 662 outputs a signal 684 tothe gate drive component 628 that generates the gate-drive signals 640and 641. In yet another example, the signal 676 is used to adjust thepulse width of the gate-drive signals 640 and 641. In yet anotherexample, the gate-drive signal 640 is the same as the gate-drive signal641.

In one embodiment, the following equation is satisfied for the closeloop configuration as shown in FIG. 6.

$\begin{matrix}{{Limit}_{N->\infty}{\quad{\left( {{\sum\limits_{i = 0}^{N}\; {\left( {{I_{pri\_ p}(i)} + {I_{{pri\_}0}(i)}} \right) \times {T_{demag}(i)}}} - {\sum\limits_{i = 0}^{N}\; {I_{ref} \times {T_{s}(i)}}}} \right) < \alpha}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

where i represents the i^(th) switching cycle, and α represents apredetermined threshold.

In another embodiment, if an output current 637 is in the range fromzero to a predetermined maximum current, the power conversion system 600operates in a constant voltage (CV) mode. For example, in the CV mode,the output voltage 636 is equal to a predetermined maximum voltage. Inanother example, if the output voltage is below the predeterminedmaximum voltage, the power conversion system 600 operates in a constantcurrent (CC) mode. In yet another example, in the CC mode, the outputcurrent 637 is equal to the predetermined maximum current.

In yet another embodiment, in the CV mode, the signal 678 generated bythe low pass filter 612 has a high magnitude. For example, the currentregulation loop does not affect the signal 684 much in the CV mode. Inanother example, in the CC mode, since the output voltage 636 is lowerthan the predetermined maximum voltage, the feedback signal 638 has ahigh magnitude. In yet another example, in the CC mode, the signal 684is not affected much by the voltage regulation process, but is affectedby the current regulation loop.

In yet another embodiment, the oscillator 634 receives the feedbacksignal 638 and the signal 678 generated from the low pass filter 612 andoutputs a clock signal 690 to the logic control component 662 formodulating the switching frequency in order to improve efficiency underdifferent output load conditions.

Similar to what is discussed in FIG. 5, demagnetization detection in thepower conversion system 600 can be achieved based on informationassociated with the voltage signal 630 at the terminal 694 (e.g.,terminal SD). Because the voltage signal 630 often changes withdifferent AC inputs or different transistors used as the switch 616, itis not easy to detect demagnetization based on absolute magnitudes ofthe voltage signal 630.

Referring back to FIG. 5, the slope of V_(SD)) is almost constant ordecreases slowly (e.g., as shown by the waveform 506) during thedemagnetization process, while at the end of the demagnetization process(e.g., at t₁₃), the slope of V_(SD)) drops rapidly. Thus, the slope ofthe voltage signal 630 can be used for demagnetization detectionaccording to certain embodiments.

FIG. 7 is a simplified diagram showing certain components of thedemagnetization component 660 as part of the power conversion system 600according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The demagnetizationcomponent 660 includes a capacitor 702, two resistors 704 and 706, acomparator 708, a blanking component 710, a timing control component712, two flip-flop components 714 and 719, a NOT gate 716, and an ANDgate 718.

According to one embodiment, the voltage signal 630 (e.g., V_(SD)) isreceived at the capacitor 702. For example, the slope of the voltagesignal 630 is detected using a differentiator including the capacitor702 and the resistors 704 and 706. In another example, a differentiatedsignal 720 is generated, and is equal to the slope of the voltage signal630 plus a direct-current (DC) offset V_(m). In yet another example, theDC offset V_(m) is determined based on the following equation.

$\begin{matrix}{V_{m} = {V_{{ref}\; 1} \times \frac{R_{4}}{R_{3} + R_{4}}}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$

where V_(m) represents the DC offset, V_(ref1) represents a referencevoltage 724, R₃ represents the resistance of the resistor 704, and R₄represents the resistance of the resistor 706.

According to another embodiment, the comparator 708 receives thedifferentiated signal 720 and a threshold signal 722 and outputs acomparison signal 726 to the blanking component 710 to affect theflip-flop components 714 and 716. For example, the gate-drive signal 640is received by the blanking component 710 and the timing controlcomponent 712 to affect the flip-flop components 714 and 716. In anotherexample, for each switching cycle, a demagnetization process starts whenthe switch 616 or 618 is open (e.g., off) in response to the gate-drivesignal 640 or 641 respectively. In yet another example, during thedemagnetization process, the differentiated signal 720 is no less thanthe threshold signal 722 in magnitude. In yet another example, if thedifferentiated signal 720 becomes smaller than the threshold signal 722in magnitude, then the end of the demagnetization process is detected.In yet another example, the comparator 708 changes the comparison signal726 in order to change the demagnetization-detection signal 666. In yetanother example, the gate-drive signal 641 can be used to replace thegate-driving signal 640.

FIG. 8( a) is a simplified timing diagram for the demagnetizationdetection component 660 as part of the power conversion system 600operating in the discontinuous conduction mode (DCM) according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications.

The waveform 802 represents the gate-drive signal 640 as a function oftime, the waveform 804 represents the voltage signal 630 as a functionof time, the waveform 806 represents the differentiated signal 720 as afunction of time, and the waveform 808 represents thedemagnetization-detection signal 666 as a function of time. For example,an on-time period starts at time t₁₄ and ends at time t₁₅, ademagnetization period, T_(demag), starts at the time t₁₅ and ends attime t₁₆, and a switching period, T_(s), starts at the time t₁₄ and endsat time t₁₇. In another example, t₁₄≦t₁₅≦t₁₆≦t₁₇.

According to one embodiment, during the on-time period, the gate-drivesignal 640 is at a logic high level (e.g., as shown by the waveform802). For example, the switch 616 is closed (e.g., on). In anotherexample, at the end of the on-time period (e.g., at t₁₅), the gate-drivesignal 640 changes from the logic high level to a logic low level (e.g.,as shown by the waveform 802), and the switch 616 is open (e.g., off).In yet another example, the demagnetization period, T_(demag), startsthen.

According to another embodiment, during the demagnetization periodT_(demag), the gate-drive signal 640 remains at the logic low level(e.g., as shown by the waveform 802). For example, the voltage signal630 (e.g., V_(SD)) keeps approximately at a magnitude 810 (e.g., asshown by the waveform 804). In another example, the differentiatedsignal 720 is larger than the threshold signal 722 in magnitude (e.g.,as shown by the waveform 806). In yet another example, thedemagnetization-detection signal 666 keeps at the logic high level(e.g., as shown by the waveform 808).

According to yet another embodiment, at the end of the demagnetizationperiod (e.g., at t₁₆), the voltage signal 630 (e.g., V_(SD)) decreasesrapidly from the magnitude 810 (e.g., as shown by the waveform 804). Forexample, the differentiated signal 720 becomes smaller than thethreshold signal 722 in magnitude (e.g., as shown by the waveform 806).In another example, the comparator 708 changes the comparison signal 726in response, and the demagnetization-detection signal 666 changes fromthe logic high level to the logic low level (e.g., as shown by thewaveform 808).

FIG. 8( b) is a simplified timing diagram for the demagnetizationdetection component 660 as part of the power conversion system 600operating in the continuous conduction mode (CCM) according to anotherembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications.

The waveform 822 represents the gate-drive signal 640 as a function oftime, the waveform 824 represents the voltage signal 630 as a functionof time, the waveform 826 represents the differentiated signal 720 as afunction of time, and the waveform 828 represents thedemagnetization-detection signal 666 as a function of time.

For example, an on-time period starts at time t₁₈ and ends at time t₁₉,and a demagnetization period, T_(demag), starts at the time t₁₉ and endsat time t₂₀. In another example, t₁₈≦t₁₉≦t₂₀.

Similar to FIG. 8( a), the demagnetization period starts when thegate-drive signal 640 changes from the logic high level to a logic lowlevel (e.g., as shown by the waveform 822), and the switch 616 is open(e.g., off), according to certain embodiments. For example, during thedemagnetization period, the voltage signal 630 (e.g., V_(SD)) keepsapproximately at a magnitude 830 (e.g., as shown by the waveform 824).In yet another example, the differentiated signal 720 is larger than thethreshold signal 722 in magnitude (e.g., as shown by the waveform 826).In yet another example, the demagnetization-detection signal 666 keepsat the logic high level (e.g., as shown by the waveform 828).

In another embodiment, at the end of the demagnetization period (e.g.,at t₂₀), the voltage signal 630 (e.g., V_(SD)) decreases rapidly fromthe magnitude 830 (e.g., as shown by the waveform 824). For example, thedifferentiated signal 720 becomes smaller than the threshold signal 722in magnitude (e.g., as shown by the waveform 826). In another example,the comparator 708 changes the comparison signal 726 in response, andthe demagnetization-detection signal 666 changes from the logic highlevel to the logic low level (e.g., as shown by the waveform 828).

FIG. 9 is a simplified diagram showing certain components of the signalprocessing component 620 as part of the power conversion system 600according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The signal processingcomponent 620 includes a timing component 902, three switches 904, 908and 910, a capacitor 906, and a gain stage 912.

According to one embodiment, during each switching cycle, if thegate-drive signal 640 changes from a logic low level to a logic highlevel, the current sensing signal 632 increases (e.g., linearly) inmagnitude from an initial value. For example, in the CCM mode, theinitial value is larger than zero. In another example, in the CRM modeor the DCM mode, the initial value is equal to zero.

According to another embodiment, the timing component 902 receives thegate-drive signal 640 and generates a control signal 914 to drive theswitch 904 for sampling the current sensing signal 632. For example,during each switching cycle, the switch 904 is closed (e.g., on), inresponse to the control signal 914, in the middle of the on-time period(e.g., at ½ T_(on)) to sample the current sensing signal 632. In anotherexample, the sampled signal (e.g., V_(s)) is held at the capacitor 906.In yet another example, the sampled signal (e.g., V_(s)) is equal, inmagnitude, to the current sensing signal 632 in the middle of theon-time period (e.g., at ½ T_(on)), and thus is determined based on thefollowing equation.

$\begin{matrix}{V_{s} = {\frac{1}{2} \times \left( {V_{{cs\_}0} + V_{{cs\_}1}} \right)}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$

where V_(s) represents the sampled signal, V_(cs) _(—0) represents themagnitude of the current sensing signal 632 when the on-time periodstarts, and V_(cs) _(—) ₁ represents the magnitude of the currentsensing signal 632 when the on-time period ends.

According to yet another embodiment, the demagnetization-detectionsignal 666 is received by a NOT gate 990 which generates a signal 914.For example, the signal 914 is at a logic low level when thedemagnetization-detection signal 666 is at a logic high level. Inanother example, the signal 914 is at the logic high level when thedemagnetization-detection signal 666 is at the logic low level. In yetanother example, during a demagnetization process, thedemagnetization-detection signal 666 is at the logic high level, and theswitch 908 is closed (e.g., on) in response to thedemagnetization-detection signal 666 to output the sampled signal (e.g.,V_(s)). In yet another example, at any time other than thedemagnetization period during the switching cycle, the signal 914 is atthe logic high level and the switch 910 is closed (e.g., on) in responseto the signal 914 to output a chip-ground voltage. Thus, an average of asignal 916 received by the gain stage 912 is determined based on thefollowing equation according to certain embodiments.

$\begin{matrix}{V_{ave} = {{\frac{1}{T_{s}} \times \left( {{V_{s} \times T_{demag}} + {0 \times T_{demag\_ b}}} \right)} = {\frac{1}{2} \times \left( {V_{{cs\_}0} + V_{{cs\_}1}} \right) \times \frac{T_{demag}}{T_{s}}}}} & \left( {{Equation}\mspace{14mu} 11} \right)\end{matrix}$

where V_(ave) represents the average of the signal 916, T_(s) representsa switching period, T_(demag) represents the demagnetization period, andT_(demag) _(—) _(b) represents the switching period excluding thedemagnetization period.

FIG. 10 is a simplified diagram showing certain components of the lowpass filter 612 as part of the power conversion system 600 according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the low pass filter 612 includes anamplifier 1002, three resistors 1004, 1006 and 1008, and a capacitor1010. In another example, the capacitor 1010 is external to thecontroller 602. In yet another example, an opto-coupler 1012 is part ofthe isolated feedback component 610. In yet another example, a currentregulation loop includes the demagnetization detection component 660,the signal processing component 620, the transconductance amplifier 624,the capacitor 626, and the low pass filter 612. In yet another example,a comparator 1098 is part of the voltage regulation component 664.

According to one embodiment, in the CV mode, an output current issmaller than the predetermined maximum current in magnitude. Forexample, the signal 1018 (e.g., V_(c)) has a large magnitude. In anotherexample, the amplifier 1002 receives the signal 1018 and outputs to theresistor 1004 an amplified signal 1014 which has a large magnitude. Inyet another example, the resistor 1004 is connected to the opto-coupler1012 and operates as a load of the opto-coupler 1012. In yet anotherexample, a feedback signal 1016 is generated at the terminal 698 (e.g.,terminal FB). In yet another example, the comparator 614 receives asignal 1020 from the resistors 1006 and 1008 and a signal 1022 from theslope compensation component 615, and outputs a comparison signal 1024for driving the switches 616 and 618. In yet another example, thecomparison signal 1024 is affected by the feedback signal 1016. In yetanother example, the signal 1018 is the same as the signal 676. In yetanother example, the feedback signal 1016 is the same as the signal 638.In yet another example, the signal 1024 is the same as the signal 682.In yet another example, the signal 1020 is the same as the signal 678.

According to another embodiment, in the CC mode, an output voltage issmaller than the predetermined maximum voltage in magnitude. Forexample, a current flowing through the collector of the opto-coupler1012 has a low magnitude (e.g., zero). In another example, the feedbacksignal 1016 is affected by the current regulation loop. In yet anotherexample, the comparator 614 changes the comparison signal 1024 based oninformation associated with the feedback signal 1016 to regulate theoutput current. In yet another example, the resistors 1004, 1006 and1008 and the capacitor 1010 perform as part of the low pass filter 612.

As shown in FIG. 10, the current regulation loop that includes thedemagnetization detection component 660, the signal processing component620, the transconductance amplifier 624, the capacitor 626 and the lowpass filter 612 shares terminal 698 (e.g., terminal FB) with the voltageregulation loop that includes the opto-coupler 1012 and the capacitor1010, according to certain embodiments. For example, both the currentregulation loop and the voltage regulation loop implement the comparator614, the logic control component 662 and the gate drive component 628 toaffect the gate-drive signals 640 and 641 in order to achieve constantcurrent regulation and constant voltage regulation respectively.

As discussed above and further emphasized here, FIG. 10 is merelyexamples, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, certain components may be included inthe controller to perform different functions, such as level shiftingand blocking, as shown in FIG. 11.

FIG. 11 is a simplified diagram showing certain components of the lowpass filter 612 as part of the power conversion system 600 according toanother embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, compared with the controller 602 shownin FIG. 10, the controller 1100 further includes three diodes 1102, 1104and 1106, and two resistors 1108 and 1110 to perform various functions,including level shifting and blocking.

FIG. 12 is a simplified diagram showing certain components of acontroller according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The controller 1200 includes a demagnetization detection component 1202,a NOT gate 1204, two current-mirror components 1206 and 1208, twoswitches 1226 and 1228, a capacitor 1210, a voltage generator 1212, twocomparators 1214 and 1218, a flip-flop component 1216, aleading-edge-blanking (LEB) component 1220, a gate drive component 1224,and a logic control component 1222. The controller 1200 further includesa terminal 1236. For example, the demagnetization detection component1202, the leading-edge-blanking (LEB) component 1220, the gate drivecomponent 1224, and the logic control component 1222 are the same as thedemagnetization detection component 660, the leading-edge-blanking (LEB)component 622, the gate drive component 628, and the logic controlcomponent 662.

The controller 1200 is used to replace at least part of the controller602 for the power conversion system 600 in some embodiments. Forexample, after the power conversion system 600 starts, the gate drivecomponent 1224 outputs gate-drive signals 1230 and 1232 to turn on theswitches 616 and 618 respectively. In another example, a primary currentbegins to flow through the primary winding 604. In yet another example,the comparator 1218 receives a current sensing signal 1234 that isrelated to the primary current and outputs a comparison signal 1240. Inyet another example, if the current sensing signal 1234 is larger than athreshold signal 1238 in magnitude, the comparator 1218 changes thecomparison signal 1240 in order to turn off the switches 616 and 618. Inyet another example, the signals 1230 and 1232 are the same as thesignals 640 and 641 respectively. In yet another example, the signal1234 is the same as the signal 632.

In another embodiment, if the switches 616 and 618 are open (e.g., off),a demagnetization process begins. For example, a secondary current thatflows through the secondary winding 606 decreases in magnitude (e.g.,linearly). In another example, the demagnetization detection component1202 receives a voltage signal 1242 (e.g., Vsp) related to a switchingnode and the gate-drive signal 1230 and generates ademagnetization-detection signal 1244.

In yet another embodiment, during the demagnetization process, thedemagnetization detection component 1202 generates thedemagnetization-detection signal 1244 at a logic high level. Forexample, the switch 1228 is closed (e.g., on) in response to the signal1244. In another example, the current-mirror component 1208 dischargesthe capacitor 1210, and a voltage signal 1246 at the capacitor 1210decreases in magnitude (e.g., linearly). In yet another example, at theend of the demagnetization process, the demagnetization detectioncomponent 1202 changes the demagnetization-detection signal 1244 fromthe logic high level to a logic low level, and the switch 1226 is closed(e.g., on) in response. In yet another example, the current-mirrorcomponent 1206 charges the capacitor 1210, and the voltage signal 1246increases in magnitude (e.g., linearly). In yet another example, if thevoltage signal 1246 is larger in magnitude than a reference voltage 1248generated by the voltage generator 1212, the comparator 1214 outputs thecomparison signal 1250 at the logic high level. In yet another example,in response, the gate drive component 1224 outputs the gate-drivesignals 1230 and 1232 to turn on the switches 616 and 618 respectively.

Thus, in some embodiments, a switching period of the power conversionsystem 600 with the controller 1200 can be determined based on thefollowing equation:

$\begin{matrix}{T_{s} = {\frac{I_{0} + I_{1}}{I_{1}} \times T_{demag}}} & \left( {{Equation}\mspace{14mu} 12} \right)\end{matrix}$

where T_(s) represents the switching period, T_(demag) represents thedemagnetization period, I₀ represents a current that flows through thecurrent-mirror component 1206, and I₁ represents a current that flowsthrough the current-mirror component 1208.

In another embodiment, a peak value of the primary current that flowsthrough the primary winding 604 is determined based on the followingequation:

$\begin{matrix}{I_{p} = \frac{V_{thoc}}{R_{s}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$

where I_(p) represents the peak value of the primary current, V_(thoc)represents the threshold signal 1238, and R_(s) represents theresistance of the resistor 608.

Assuming the transformer including the primary winding 604 and thesecondary winding 606 has a transfer efficiency of 100%, an outputcurrent of the power conversion system 600 can be determined based onthe following equation in some embodiments.

$\begin{matrix}{I_{out} = \frac{\frac{1}{2} \times N \times I_{p} \times T_{demag}}{T_{s}}} & \left( {{Equation}\mspace{14mu} 14} \right)\end{matrix}$

where I_(out) represents the output current, and N represents the turnsratio between the primary winding 604 and the secondary winding 606. Forexample, combining Equations 12, 13 and 14, the output current can bedetermined based on the following equation:

$\begin{matrix}{I_{out} = {\frac{1}{2} \times \frac{I_{1}}{I_{0} + I_{1}} \times \frac{V_{thoc}}{R_{s}}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

Thus, the output current can be controlled to be a constant currentaccording to certain embodiments.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal, a secondcontroller terminal and a third controller terminal. The systemcontroller is configured to receive an input signal at the firstcontroller terminal and turn on or off a switch based on at leastinformation associated with the input signal to adjust a primary currentflowing through a primary winding of the power conversion system,receive a first signal at the second controller terminal from theswitch, and charge a capacitor through the third controller terminal inresponse to the first signal. For example, the system controller isimplemented according to at least FIG. 4( a) and/or FIG. 4( b).

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. The system controller is configured togenerate a drive signal at the first controller terminal to turn on oroff a switch to adjust a primary current flowing through a primarywinding of the power conversion system, receive a first signal at thesecond controller terminal from the switch, and generate a detectionsignal associated with a demagnetization process of the primary windingof the power conversion system based on at least information associatedwith the first signal. For example, the system controller is implementedaccording to FIG. 4( a), FIG. 4( b), FIG. 5, FIG. 6, FIG. 7, FIG. 8( a),FIG. 8( b), FIG. 9, FIG. 10, FIG. 11 and/or FIG. 12.

According to yet another embodiment, a system for regulating a powerconversion system includes a system controller, a feedback component anda capacitor. The system controller includes a current regulationcomponent and a drive component, the system controller further includinga first controller terminal connected to the current regulationcomponent and a second controller terminal connected to the drivecomponent. The feedback component is connected to the first controllerterminal and configured to receive an output signal associated with asecondary winding of a power conversion system. The capacitor includes afirst capacitor terminal and a second capacitor terminal, the firstcapacitor terminal being connected to the first controller terminal. Thecurrent regulation component is configured to receive at least a currentsensing signal and affect a feedback signal at the first controllerterminal based on at least information associated with the currentsensing signal, the current sensing signal being associated with aprimary current flowing through a primary winding of the powerconversion system. The drive component is configured to processinformation associated with the current sensing signal and the feedbacksignal, generate a drive signal based on at least information associatedwith the current sensing signal and the feedback signal, and send thedrive signal to a switch through the second controller terminal in orderto adjust the primary current. For example, the system controller isimplemented according to at least FIG. 10 and/or FIG. 11.

In another embodiment, a method for regulating a power conversion systemby at least a system controller including a first controller terminal, asecond controller terminal and a third controller terminal includes:receiving an input signal at the first controller terminal, turning onor off a switch based on at least information associated with the inputsignal to adjust a primary current flowing through a primary winding ofthe power conversion system, receiving a first signal at the secondcontroller terminal from the switch, and charging a capacitor throughthe third controller terminal in response to the first signal. Forexample, the method is implemented according to at least FIG. 4( a)and/or FIG. 4( b).

In yet another embodiment, a method for regulating a power conversionsystem by at least a system controller including a first controllerterminal and a second controller terminal include: generating a drivesignal at the first controller terminal to turn on or off a switch toadjust a primary current flowing through a primary winding of the powerconversion system, receiving a first signal at the second controllerterminal from the switch, and generating a detection signal associatedwith a demagnetization process of the primary winding of the powerconversion system based on at least information associated with thefirst signal. For example, the method is implemented according to FIG.4( a), FIG. 4( b), FIG. 5, FIG. 6, FIG. 7, FIG. 8( a), FIG. 8( b), FIG.9, FIG. 10, FIG. 11 and/or FIG. 12.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for regulating a powerconversion system, the system controller comprising: a first controllerterminal; a second controller terminal; and a third controller terminal;wherein the system controller is configured to: receive an input signalat the first controller terminal and turn on or off a switch based on atleast information associated with the input signal to adjust a primarycurrent flowing through a primary winding of the power conversionsystem; receive a first signal at the second controller terminal fromthe switch; and charge a capacitor through the third controller terminalin response to the first signal.
 2. The system controller of claim 1wherein the first controller terminal is connected, directly orindirectly to a resistor, the resistor being configured to receive athird signal associated with an AC signal received by the powerconversion system and output the input signal to the first controllerterminal based on at least information associated with the third signal.3. The system controller of claim 1 wherein the second controllerterminal is connected, directly or indirectly to a diode, the diodeincluding an anode terminal and a cathode terminal; wherein: the anodeterminal is connected, directly or indirectly, to the second controllerterminal; and the cathode terminal is connected, directly or indirectly,to the third controller terminal.
 4. The system controller of claim 3,and further comprising: a resistor including a first resistor terminaland a second resistor terminal; wherein: the first resistor terminal isconnected to the anode terminal; and the second resistor terminal isconnected to the second controller terminal.
 5. The system controller ofclaim 1 wherein the switch is part of the system controller.
 6. Thesystem controller of claim 1, and further comprising: acurrent-regulating component configured to receive at least the firstsignal at the second controller terminal and generate a detection signalassociated with a demagnetization process of the primary winding of thepower conversion system based on at least information associated withthe first signal.
 7. A system controller for regulating a powerconversion system, the system controller comprising: a first controllerterminal; and a second controller terminal; wherein the systemcontroller is configured to: generate a drive signal at the firstcontroller terminal to turn on or off a first switch to adjust a primarycurrent flowing through a primary winding of the power conversionsystem; receive a first signal at the second controller terminal fromthe first switch; and generate a detection signal associated with ademagnetization process of the primary winding of the power conversionsystem based on at least information associated with the first signal.8. The system controller of claim 7, and further comprising: a secondswitch; and a third controller terminal; wherein the second switch isconfigured to receive the first signal at the second controller terminaland a current sensing signal at the third controller terminal and beturned on or off based on at least information associated with the drivesignal, the current sensing signal being associated with a primarycurrent flowing through the primary winding of the power conversionsystem.
 9. The system controller of claim 8 wherein the second switch isfurther configured to be turned on when the first switch is turned onand be turned off when the first switch is turned off.
 10. The systemcontroller of claim 9 wherein the system controller is furtherconfigured to generate the detection signal based on at leastinformation associated with a change rate of the first signal.
 11. Thesystem controller of claim 10 wherein the change rate of the firstsignal reduces at the end of the demagnetization process.
 12. The systemcontroller of claim 9, and further comprising a demagnetization detectorconfigured to receive the drive signal and the first signal and generatethe detection signal based on at least information associated with thedrive signal and the first signal.
 13. The system controller of claim 12wherein: the demagnetization detector is further configured to generatethe detection signal at a first logic level if the primary windingoperates in the demagnetization process; and the demagnetizationdetector is further configured to generate the detection signal at asecond logic level if the primary winding does not operate in thedemagnetization process.
 14. The system controller of claim 13 whereinthe first switch is turned on or off at a switching frequency, aswitching period associated with the switching frequency including anon-time period and an off-time period, the first switch being turned onduring the on-time period and being turned off during the off-timeperiod.
 15. The system controller of claim 14, and further comprising: afirst signal processing component configured to receive the currentsensing signal associated with the primary current and the detectionsignal associated with the demagnetization process, and generate a firstprocessed signal based on at least information associated with thecurrent sensing signal and the detection signal; a second signalprocessing component configured to receive a reference voltage signaland a clock signal, and generate a second processed signal based on atleast information associated with the reference voltage signal and theclock signal; and an error amplifier configured to receive the firstprocessed signal and the second processed signal and output an amplifiedsignal based on at least information associated with the first processedsignal and the second processed signal in order to adjust the drivesignal.
 16. The system controller of claim 15, and further comprising: alow pass filter configured to receive the amplified signal and generatea filtered signal based on at least information associated with theamplified signal; and a comparator configured to receive the filteredsignal and the current sensing signal and output a modulation signalbased on at least information associated with the filtered signal andthe current sensing signal in order to adjust the drive signal toachieve constant current regulation.
 17. The system controller of claim15 wherein the first signal processing component includes: a sample andhold component configured to sample and hold the current-sensing signalat a middle point of an on-time period during each switching period; asignal selection component configured to output the held sampledcurrent-sensing signal if the detection signal is at the second logiclevel, and output a ground voltage if the detection signal is at thefirst logic level; and an amplifying component configured to receive theheld sampled current-sensing signal or the ground voltage and output thefirst processed signal.
 18. The system of claim 17 wherein the sampleand hold component includes: a timing component configured to receivethe drive signal and generate a sampled current-sensing signal at themiddle point of the on-time period during each switching period; and acapacitor configured to hold the sampled current-sensing signal.
 19. Thesystem controller of claim 13 wherein the demagnetization detectorincludes: a differentiation component configured to receive the firstsignal and output a differentiated signal based on at least informationassociated with the first signal; a comparator configured to receive atleast the differentiated signal and generate a comparison signal; and adetection component configured to receive the comparison signal and thedrive signal and output the detection signal based on at leastinformation associated with the comparison signal and the drive signal.20. The system controller of claim 19 wherein the differentiationcomponent includes: a capacitor including a first capacitor terminal anda second capacitor terminal; a first resistor including a first resistorterminal and a second resistor terminal; and a second resistor includinga third resistor terminal and a fourth resistor terminal; wherein: thefirst resistor terminal is biased to a first predetermined voltage; thesecond resistor terminal is connected to the third resistor terminal;the second capacitor terminal is connected to the second resistorterminal; and the fourth resistor terminal is biased to a secondpredetermined voltage; wherein: the first capacitor terminal isconfigured to receive the first signal; and the second resistor terminalis configured to output the differentiated signal.
 21. The systemcontroller of claim 13, and further comprising: anoutput-current-regulation component configured to receive the detectionsignal, generate a first predetermined current if the detection signalis at the first logic level, and generate a second predetermined currentif the detection signal is at the second logic level.
 22. The systemcontroller of claim 21, and further comprising: a capacitor configuredto be charged with the first predetermined current if the detectionsignal is at the first logic level and be discharged with the secondpredetermined current if the detection signal is at the second logiclevel.
 23. The system controller of claim 22, and further comprising: afirst comparator configured to receive a voltage signal from thecapacitor and a reference signal and outputs a first comparison signalbased on at least information associated with the voltage signal and thereference signal; wherein: if the voltage signal is larger than thereference signal in magnitude, the first comparator is furtherconfigured to change the first comparison signal in order to change thedrive signal.
 24. The system controller of claim 23, and furthercomprising: a second comparator configured to receive the currentsensing signal and a threshold signal and output a second comparisonsignal based on at least information associated with the current sensingsignal and the threshold signal; and a flip-flop component configured toreceive the first comparison signal and the second comparison signal andgenerate an output signal in order to generate the drive signal.
 25. Asystem for regulating a power conversion system, the system comprising:a system controller including a current regulation component and a drivecomponent, the system controller further including a first controllerterminal connected to the current regulation component and a secondcontroller terminal connected to the drive component; a feedbackcomponent connected to the first controller terminal and configured toreceive an output signal associated with a secondary side of a powerconversion system; and a capacitor including a first capacitor terminaland a second capacitor terminal, the first capacitor terminal beingconnected, directly or indirectly, to the first controller terminal;wherein: the current regulation component is configured to receive atleast a current sensing signal and affect a feedback signal at the firstcontroller terminal based on at least information associated with thecurrent sensing signal, the current sensing signal being associated witha primary current flowing through a primary winding of the powerconversion system; and the drive component is configured to processinformation associated with the current sensing signal and the feedbacksignal, generate a drive signal based on at least information associatedwith the current sensing signal and the feedback signal, and provide thedrive signal to a switch through the second controller terminal in orderto adjust the primary current.
 26. The system of claim 25 wherein thecurrent regulation component includes: a signal processing componentconfigured to receive at least the current sensing signal, and generatea processed signal based on at least information associated with thecurrent sensing signal; an error amplifier configured to receive theprocessed signal and a reference signal and generate a first amplifiedsignal based on at least information associated with the processedsignal and the reference signal; and a low pass filter configured toreceive the first amplified signal and generate a filtered signal basedon at least information associated with the first amplified signal inorder to affect the drive signal.
 27. The system of claim 26 wherein thelow pass filter includes: a first amplifier including a first inputamplifier terminal, a second input amplifier terminal and an outputamplifier terminal; and a first resistor including a first resistorterminal and a second resistor terminal; wherein: the second inputamplifier terminal is connected to the output amplifier terminal; thefirst resistor terminal is connected to the output amplifier terminal;the second resistor terminal is connected, directly or indirectly, tothe first capacitor terminal; the first amplifier is configured toreceive at least the first amplified signal at the first input amplifierterminal and generate a second amplified signal based on at leastinformation associated with the first amplified signal in order toaffect the feedback signal; and the first amplified signal is associatedwith the current sensing signal.
 28. The system of claim 27 wherein thedrive component includes: a second resistor including a third resistorterminal and a fourth resistor terminal; and a third resistor includinga fifth resistor terminal and a sixth resistor terminal; wherein: thethird resistor terminal is connected, directly or indirectly, to thesecond resistor terminal; the fourth resistor terminal is connected tothe fifth resistor terminal; and the sixth resistor terminal is biasedto a predetermined voltage; and the drive component is configured togenerate a voltage signal at the fourth resistor terminal based on atleast information associated with the feedback signal in order to affectthe drive signal.
 29. The system of claim 28, and further comprising adiode including a first diode terminal and a second diode terminal, thefirst diode terminal being connected to the second resistor terminal andthe second diode terminal being connected to the third resistorterminal.
 30. A method for regulating a power conversion system by atleast a system controller including a first controller terminal, asecond controller terminal and a third controller terminal, the methodcomprising: receiving an input signal at the first controller terminal;turning on or off a switch based on at least information associated withthe input signal to adjust a primary current flowing through a primarywinding of the power conversion system; receiving a first signal at thesecond controller terminal from the switch; and charging a capacitorthrough the third controller terminal in response to the first signal.31. A method for regulating a power conversion system by at least asystem controller including a first controller terminal and a secondcontroller terminal, the method comprising: generating a drive signal atthe first controller terminal to turn on or off a first switch to adjusta primary current flowing through a primary winding of the powerconversion system; receiving a first signal at the second controllerterminal from the first switch; and generating a detection signalassociated with a demagnetization process of the primary winding of thepower conversion system based on at least information associated withthe first signal.
 32. The method of claim 31, and further comprising:receiving the detection signal; receiving a current sensing signal at athird controller terminal of the system controller, the current sensingsignal being associated with a primary current flowing through theprimary winding of the power conversion system; generating a firstprocessed signal based on at least information associated with thecurrent sensing signal and the detection signal; receiving a referencevoltage signal and a clock signal; generating a second processed signalbased on at least information associated with the reference voltagesignal and the clock signal; receiving the first processed signal andthe second processed signal; generating an amplified signal based on atleast information associated with the first processed signal and thesecond processed signal; receiving the amplified signal; generating afiltered signal based on at least information associated with theamplified signal; receiving the filtered signal and the current sensingsignal; and outputting a modulation signal based on at least informationassociated with the filtered signal and the current sensing signal toadjust the drive signal in order to achieve constant current regulation.